Within the contact group of sulfuric acid plants tube bundle heat exchangers usually are employed, which are installed in a vertical configuration, so that possibly obtained sulfuric acid condensate can flow off towards the bottom tray and can be withdrawn there to avoid corrosion. In general, the SO2 gas is guided on the casing side and the SO2/SO3 gas is guided on the tube side. In commercial plants over 1,500 tato MH, disk-and-doughnut heat exchangers are used (cf. Winnacker/Küchler, Chemische Technik: Prozesse and Produkte, edited by Roland Dittmeyer et al., Vol. 3: Anorganische Grundstoffe, Zwischenprodukte, p. 96 f., Wiley-VCH Verlag, Weinheim, 2005).
The cold SO2 gas generally is guided in counterflow to the SO3-containing gas to be cooled. It was found out that the sulfuric acid condensate leads to a strong corrosion in particular in the first chamber of the heat exchanger, so that high-alloy and expensive stainless steel materials must be used. To reduce the costs, the heat exchanger was divided into two parts, so that in the case of excessive corrosion not the entire heat exchanger, but merely the region exposed to cold gas, in which a particularly high corrosion occurs, must be replaced. While initially assuming a uniform division of the heat transfer region, the applicant recently has employed heat exchangers in which in the cold heat-exchange section (1st chamber) only a minor part of the entire heat transfer surface was provided. Moreover, instead of an arrangement in which two vertically oriented heat exchangers are arranged one beside the other and which creates problems in terms of drainage, there was now used an arrangement in which the chamber, to which the cold SO2 gas is supplied, is arranged horizontally. From this first chamber, the sulfuric acid condensate can simply be withdrawn at the bottom. The SO2-containing gas then was transferred into the adjoining vertical section with a greater heat transfer surface. It was found out, however, that in the case of the radial approach flow of the tube bundle in the horizontal section of the heat exchanger a non-uniform gas flow and as a result an impairment of the heat transfer can occur.